This invention relates to piezoresistive sensors, and more particularly, to a stopped leadless differential pressure sensor.
As indicated, the above-noted application entitled, xe2x80x9cDouble Stop Structure for a Pressure Transducerxe2x80x9d depicts the problem of utilizing stops on a differential pressure transducer. A differential pressure transducer is a device which provides an output which is the difference between two input pressures. For example, when a pressure P1 is applied to one phase of the deflecting member and a pressure P2 is applied to the other face of the deflecting member, the resulting deflection will be determined by the difference in pressure, as for example for example, P1 minus P2. An example of differential piezoresistive bridge pressure transducers is illustrated in U.S. Pat. No. 6,272,928 entitled, xe2x80x9cHermetically Sealed Absolute and Differential Pressure Transducersxe2x80x9d assigned to the assignee herein. In any event, the above-noted application describes the problems and the need for a stop structure that provides improved stopping capabilities, while ensuring adequate pressure application to the sensor structure. As one can ascertain, there remains a need for a stop structure that provides apertures that are large enough to ensure adequate pressure application, while providing apertures that are small enough to ensure the best stopping. There has also been improved pressure transducers, which are now in widespread use and which need to be stopped in both directions as employed in a differential pressure configuration.
The improvement of semiconductor transducers has increased and there is a series of transducers which have been innovated by the assignee herein and referred to as leadless transducers. See for example, U.S. Pat. No. 5,973,590 which issued on Oct. 26, 1999 entitled, xe2x80x9cUltra Thin Surface Mount Wafer Sensor Structure and Methods of Fabricating the Samexe2x80x9d to A. D. Kurtz et al. and is assigned to the assignee herein. See also U.S. Pat. No. 6,210,989 which issued on Apr. 3, 2001 entitled, xe2x80x9cUltra Thin Surface Mount Wafer Sensor Structures and Methods of Fabricating the Samexe2x80x9d issued to A. D. Kurtz et al. and is assigned to the assignee herein. See also, U.S. Pat. No. 6,272,929 entitled, xe2x80x9cHigh Pressure Piezoresistive Transducer Suitable for Use in Hostile Environmentsxe2x80x9d which issued on Oct. 14, 2001 to A. D. Kurtz et al. and is assigned to the assignee herein.
Essentially, such an ultra thin surface mount or leadless transducer is a semiconductor sensor device including a semiconductor diaphragm member having a top surface coated with an oxide layer. P+ sensor elements are fusion bonded to the oxide layer at a relatively central area of the diaphragm. P+ finger elements are fusion bonded to the oxide layer and extend from the sensors to an outer contact location of the diaphragm for each finger. There is an external rim of P+ material fusion bonded to the oxide layer surrounding the sensors and fingers. A first glass wafer member is electrostatically bonded at a bottom surface to the fingers and rim to hermetically seal the sensor and fingers of the diaphragm member. The first glass wafer includes a depression above the sensors and has a plurality of apertures, where each aperture is associated with a separate finger at a contact location. Each aperture is smaller than the associated finger, which is aligned with the contact location. Each contact location can therefore be accessed via the associated aperture and the first glass member. A second glass wafer member is secured to the top surface of the first glass wafer and has a plurality of apertures aligned with the plurality of apertures of the first glass wafer member and containing a group of hermetically sealed pins for coupling to the contact locations. Essentially, it is an object of the present invention to utilize the transducer structure shown in the above-noted references as a stopped leadless differential sensor where the leadless sensor is stopped in both directions.
A leadless sensor of the type employing a p+ rim which surrounds contact areas, each contact area defined by a metallized portion surrounded by a p+ semiconductor material, which p+ semiconductor materials are coupled to an active sensor array. The leadless sensor is bonded to a first cover member having two slotted apertures which communicate with the active regions of the sensor area on the underside and a top contact member which has two slotted regions which communicate with the piezoresistive sensors on the top side of the semiconductor wafer. The contact member has a series of through holes which are congruent with the contact terminals associated with the semiconductor sensor and which through holes are filled with a glass metal frit to enable contact to be made to the contact terminals of the semiconductor sensor. The contact glass member and cover member are electrostatically bonded to the silicon sensor at both sides of the sensor and have stop structures on both members to enable the sensor to receive a force or pressure in either direction. If the force in either direction exceeds a predetermined force, the silicon sensor will impinge against the surface of the stop area to limit the force and therefore prevent damage to the sensor. The sensor behaves as a differential sensor in operation where the Wheatstone Bridge sensor array provides a difference between the force applied to the top side of the sensor with respect to the force applied to the bottom side of the sensor.